Conventional electrical AC power cable transmission may be limited in distance due to cable properties. Typical maximum AC transmission distance at 50/60 Hz may be between 100 km and 200 km. If longer distances are needed, DC transmission is used. For subsea power, it is useful to reach out farther than 200 km. For arctic areas, hydro carbon reservoirs with step outs up to 600 km from shore are explored. AC power may be used for powering consumers at a subsea exploration site, such as pumps, compressors, motors etc. Therefore, in a conventional system, the DC power transmitted to the sea ground is converted into AC power, in order to be appropriate to power the consumers at the subsea exploration site. However, converting the DC power to an AC power involves large and heavy equipment that poses a number of problems for setting up the exploration site and also increases the costs of the system. When designing a subsea power grid, reliability may be one of the main factors. To increase the reliability of a subsea power grid, it may be useful to limit the complexity and also to limit components with low reliability, such as non-redundant types of components. Only medium voltage distribution technology for AC solution may be reliable. This means that DC power is converted to AC power subsea for subsea DC transmission systems. The DC to AC converting system may be a complex system consisting of a high number of components, and may reduce reliability relative to a subsea AC transmission system.
There may be a need for a method and an arrangement for transferring electrical power in the sea, which facilitates powering of electrical AC power of subsea consumers with step out much longer than today's typical maximum transmission distance of 100-200 km. Benefits may also be provided if this increases the reliability and at the same time reduces the size of the equipment. Further, there may be a need to provide AC consumers with AC power in a simpler manner involving smaller or lighter equipment than a conventional system.